Anyone have a guide for this? I keep losing my 2nd or 3rd battle no matter who I fight
after my first battle I spent all my money on potions and barely beat her again, then i was too poor to do so again.
Potions are a trap, most of the time. Money-wise, that is. And after a tiny bit you won't need them in fights either.
There are two ways to recover health in-between fights:
1) rent a room
2) talk with the trainer dude sitting at one of the table and train to get levels
If you have the money for it, it's better to train and gain a level, then go back to fighting. Rent a room if you don't have the money for a level.
Once you get your Dominance high, talk with the Noble lady. She'll offer you money in exchange for lowering your Dominance. That can get you a lot of money.
Also, buying better equipment is important.
I'd advise you to start over with a new save, it'll be easier that way.
EDIT: After a while you'll unlock an option at the purple-haired receptionist where she proposes to make the fighting girls not take MC seriously, lowering their levels. You should absolutely take her on her offer and pay to lower at least the redhead's level to the maximum possible.
Then by that point you should be powerful enough to beat her quick, several times, without risk and without needing to heal between rounds. That'll get you a good bit of money.